Construction machinery is used in renovating, reconstructing and extending buildings, for example. Wall saws are used for cutting and extending openings for doors, windows and light wells, etc., corrective work on facades, partition walls and garden walls, etc., and controlled demolition of concrete. Floor saws are wheeled and normally used for cutting in concrete floors. Wall saws, floor saws masonry saws and similar construction machinery have a drive motor, usually electric, and a rotary tool driven by the motor. In a wall saw or floor saw, the tool is a circular saw blade equipped with cutting diamond segments. Generally, heavy duty wall saws are driven hydraulically, see U.S. Pat. No. 6,955,167 B2, US 2006/0201492 A1, US 2007/0163412 A1, and U.S. Pat. No. 5,887,579, for example. However, hydraulic wall saws are comparatively heavy and not easy to set up, and comparatively low-weight electric wall saws, such as the one disclosed in US 2006/0189258 A1, for example, have been introduced on the market. Such an electric wall saw is usually driven by an induction motor running at a specifically set rotational speed for maximum power output. The speed for maximum power output is usually in the order of magnitude between 15,000 rpm and 30,000 rpm requiring a planetary gear set or the like for reducing the speed to a suitable rotational speed for the saw blade. Planetary gears are costly and would usually require an oil pump for sufficient supply of lubrication or splash lubrication. Further, it is usually desirable to run the wall saw so that the cutting segments get a same optimal peripheral speed. Saw blades of different diameters therefore requires that the transmission ratio from the induction motor to the saw blade be variable. Since the rotational speed for maximum power output of such an induction motor is fixed, a mechanical gearbox with many gears or a variator is also required, e.g. a gearbox with one mechanical gear for each blade diameter to be used. These solutions have several drawbacks, such as being costly, heavy, and space requiring, as well as being in need of thorough service regularly.
A portable rotary cutting machine for stone is disclosed in GB 704 748 A. It has a circular saw blade and a drive motor connected to the saw blade via a transmission with an adjustable friction clutch.
JP 58-028045 A relates to a torque limiter holding an internal gear of a planetary gear speed change device through friction.
An electric-powered stone cutter having a motor and a transmission is disclosed in U.S. Pat. No. 5,653,218 A1. The motor axis is located in the plane of the saw blade, and the transmission includes an elongated drive shaft extending parallel to the saw blade for transferring the power from the motor from outside the periphery of the saw blade to the center thereof.
US 2007/0180709 A1 discloses a handheld circular saw, A motor housing supports the motor and a transmission mechanism for transferring energy from the motor to the rotary saw blade. A handle assembly is provided for moving the saw with respect to a work piece. The handle assembly is rotatable relative to the saw blade housing during operation of the motor.
DE 10 2006 018 262 (A1) relates to an electric motor for e.g. sawing of plate-shaped bodies, has disk-shaped rotor with asymmetrically arranged rotor disk, and permanent magnets fastened at rotor disk and at processing and sawing tools.
A wall saw usually includes a rack, i.e. a toothed bar or rod, intended to be attached to and equidistantly spaced from the wall or floor, which is to be sawed through. A carriage carries a drive motor for the circular saw blade and is movable along the rack by means of another motor. Normally the wall saw can be remotely controlled for safety and comfort of the operator. The saw blade is mounted at the free end of a pivotal arm attached to the carriage and housing a transmission for transferring the rotation of the drive motor shaft to the saw blade. The pivotal arm, or transmission housing, is swung towards or away from the wall by a third motor. The transmission usually includes a first gear mounted on the motor output shaft of the drive motor, and a second gear having a gear output shaft, on which the saw blade is intended to be mounted. The second gear may be drivingly connected to the first gear by a chain or, preferably, by one or more interposed gears. However, in case some unexpected event causes an immediate stop of the rotation of the exterior forces, and the teeth and gears have to be dimensioned to stand such forces. As it is difficult to know the size of such forces, the teeth and gears usually are greatly oversized.